1. Field of the Invention
The present invention relates generally to mechanized irrigation systems. In particular, the present invention relates to a GPS-based control system for determining the angular position of a center pivot irrigation system, or for determining the distance traveled by a linear move irrigation system, and using the information to control a function of the irrigation system.
2. Description of the Related Art
Mechanized sprinkler irrigation systems are widely used throughout the world to provide water for agricultural purposes in arid regions. Typically, such systems include a series of spaced support towers connected by truss sections that support an elevated water distribution pipe between the towers. In center pivot systems, the water distribution pipe extends radially from a central pivot communicating with a pressurized water supply. In linear move irrigation systems, the water distribution pipe extends laterally from a canal feed or hose drag system that provides a pressurized water supply.
Water passing through the distribution pipe is forced out through a number of sprinkler heads, spray guns, drop nozzles, and the like, spaced along the length of the pipe. Each tower in the system is supported on wheels that are driven at slow speeds to move the tower in a circular path about the central pivot, or a linear path in the case of linear move systems, to thereby irrigate a large tract of land.
Mechanized irrigation systems, particularly center pivot irrigation systems, are often provided with high pressure sprayers, known as end guns, which are mounted on the end tower. The end guns are activated at the corners of the field or other areas to increase the amount of area that can be irrigated by the irrigation system. Booster pumps are often associated with the end guns to increase the water pressure to the end gun for providing an even larger watering pattern.
A growing number of mechanized irrigation systems employ some sort of electronic controls. These controls allow the operator to program the irrigation system to operate to his specific need. Generally, these controllers can change application rate, control end gun functions, and automatically stop or reverse the system anywhere in the field. These controllers can also be used to shut off selected towers or nozzles at predetermined locations in the field or to control other functions of the sprinkler system. In the case of center pivot sprinkler systems, the system moves in a circular path and the standard positioning value to the operator is in degrees. Zero degrees (0°) is typically straight north and 180 degrees (180°) is straight south. In the case of linear move irrigation systems, the system moves in a straight path and the standard positioning value to the operator is in distance traveled from a reference point.
The current means of indicating the position of a pivot irrigation system is by mounting an encoder at the center of the pivot inside of a slip ring assembly. The encoder then only moves when the first tower from the center moves. The encoder does not provide positive feedback of when the end tower is moving. As a result, the end gun is not always activated at the most advantageous position of the end tower, and it is difficult to stop, reverse and/or change the speed of the system accurately because the exact location of the end tower is not known.
Until recently the use of Global Positioning Satellite (GPS) data to locate the end tower of a center pivot irrigation system would have been impractical from the standpoint that such position calculations were too inaccurate and GPS receiver/senders were prohibitively expensive. However, the FAA recently launched a satellite that can send corrections to any GPS receiver and decrease positioning errors to about 15 feet. The signal used by the FAA satellite is called WAAS or Wide Area Augmentation System. GPS receivers receive the WAAS signal using the same antenna as the GPS signals.
WAAS is based on a network of approximately 25 ground reference stations that cover a very large service area. Signals from GPS satellites are received by wide area ground reference stations (WRSs). Each of these precisely surveyed reference stations receives GPS signals and determines if any errors exist. These WRSs are linked to form the United States WAAS network. Each WRS in the network relays the data to the wide area master station (WMS) where correction information is computed. The WMS calculates correction algorithms and assesses the integrity of the system. A correction message is prepared and uplinked to a geosynchronous satellite via a ground uplink system (GUS). The message is then broadcast from the satellite on the same frequency as GPS (L1, 1575.42 MHz) to receivers which are within the broadcast coverage area of the WAAS.
There is a need in the industry for an improved control system that uses GPS to accurately detect the angular position of a center pivot irrigation system, or to accurately detect the distance traveled by a linear move irrigation system, and that uses such information to control various functions of the irrigation system.